As power switching elements, power metal-oxide-semiconductor field-effect transistors (i.e., MOSFETs) (hereinafter, sometimes referred to as power MOSFETs) are widely used. Among them, in order to increase the channel width density, a trench gate type MOSFET has been put into practical use, in which a trench is formed on a surface of a semiconductor wafer and a side surface of, the trench is used as a channel. In the trench gate type MOSFET, since a gate structure is formed inside the trench, it is possible to reduce the cell pitch. Therefore, it is possible to increase the performance of the device.
In recent years, as a next-generation power device of high breakdown voltage and low loss, attention is focused on a trench gate type SiC-MOSFET using silicon carbide (SiC). In most cases, in a SiC substrate used for manufacturing this type of device, an off angle is provided on a crystal plane. In a case where a trench is formed on the SiC substrate having an off angle, usually, side wall surfaces of the trench are surfaces which have different angles from the crystal axis (see, for example, Patent Document 1).